Formulation of Microemulsion gel of Zingiber Officinale extract and evaluation of anti-inflammatory activity in rats

Abstract

This investigation was aimed to evaluate the anti-inflammatory activity of ginger extract, microemulsion and microemulsion gel formulations containing ginger extract. Physicochemical characterization, stability and release studies of preparation were also performed. Extraction of ZINGIBER OFFICINALE rhizomes containing [6]-gingerol was performed by fractionation extraction with hexane followed with acetone and simple extraction with acetone. Acetone crude extract gave the highest yield of 10.97%, where hexane extract and acetone extract had 3.93 and 7.06% w/w, respectively, however they had not significantly different [6]-gingerol content of 10.70-11.44%. The anti-inflammatory activity of ginger extracts were evaluated in a carrageenan-induced rat paw edema test and compared with that of indomethacin. Rats treated with the crude extract showed the highest reduction in paw edema compared with other extracts. The lowest concentration (5% w/w) of the crude extract demonstrated the highest percentage inhibition of paw edema. Pseudo-ternary phase diagram was constructed by water titration method to find out microemulsion regions. Isopropyl myristate was used as oil phase. Nonionic surfactants with different HLB values such as Brij®30, Brij®93, Brij®97 and Cremophor RH 40 were selected. It was found that the surfactant with HLB value similar to that of oil phase could form microemulsion in absence of cosurfactant, Transcutol® CG. In the presence of cosurfactant, microemulsion area in the phase diagram increased. The optimal surfactant to cosurfactant ratio was found at 1:1. Microemulsions with water content at least 30% and surfactant mix content less than 65% were selected to prepare microemulsion gel. From electrical conductivity measurement, microemulsions obtained were oil in water type, acceptable pH and low viscosities. It was shown that all natural gum derivatives gave separated microemulsion gels, whereas certain cellulose derivatives (carboxymethylcellulose sodium) and polyacrylic derivatives (Carbopol 934, Carbopol 940) could form microemulsion gels. Incorporation of 5% w/w ginger extract into microemulsions and microemulsion gels caused slightly decrease of pH and viscosity change, but showed good stability in terms of no phase separation or precipitation of ginger extract. After 6 heating-cooling cycles, [6]-gingerol content in microemulsion and microemulsion gel decreased to 85.19-92.21% and 92.87-97.28%, respectively. Release of [6]-gingerol from microemulsions and microemulsion gels were sustained as compared with solution. The cumulative amount released of [6]-gingerol from microemulsions and microemulsion gels at 24 hour were 33.52-45.76% and 27.58-37.33%, respectively. All [6]-gingerol release profiles exhibited the best fit with Higuchi kinetics that revealed diffusion-controlled. The rate determining step was that [6]-gingerol diffused from oil phase through external aqueous phase and gel matrix. Higher viscosity of microemulsion gel retarded the release and resulted to significantly lower release rate constants than microemulsions (p0.05). In addition, surfactant types and content of surfactant mixture had significant effect to the release rate constant, whereas polymer types had no effect. The selected microemulsion gel formulation using Cremophor® RH 40 and Carbopol 940 with 5% w/w ginger extract demonstrated slower onset and longer duration of anti-inflammatory activity compared with the corresponding microemulsion.